The present invention relates generally to a method and apparatus for delivering radiation to interior sites in the human body. More specifically, the present invention relates to an intravascular catheter including a string having a radioactive section, the string being looped around a catheter distal member for advancing and retracting the radioactive string section once the catheter is positioned near a targeted site. The present invention can be used to irradiate dilated, stenosed blood vessel regions to inhibit restenosis.
Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). These therapeutic techniques are well known in the art and typically involve use of a guide wire and a balloon catheter, possibly in combination with other intravascular devices. A typical balloon catheter has an elongate shaft with a balloon attached to its distal end and a manifold attached to the proximal end. In use, the balloon catheter is advanced over the guide wire such that the balloon is positioned adjacent a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
Vascular restrictions that have been dilated do not always remain open. In approximately 30 to 50% of the cases, a restriction reappears over a period of months. The mechanism of this restenosis is not understood. The mechanism is believed to be different from the mechanism that caused the original stenosis. It is believed that rapid proliferation of vascular smooth muscle cells surrounding the dilated region may be involved. Restenosis may be in part a healing response to the dilation, including the formation of scar tissue.
Intravascular radiation, including thermal, light and radioactive radiation, has been proposed as a means to prevent or reduce the effects of restenosis. For example, U.S. Pat. No. 4,799,479 to Spears suggests that heating a dilated restriction may prevent gradual restenosis at the dilation site. In addition, U.S. Pat. No. 5,417,653 to Sahota et al. suggests that delivering relatively low energy light, following dilatation of a stenosis, may inhibit restenosis. While most clinical studies suggest that thermal radiation and light radiation are not significantly effective in reducing restenosis, some clinical studies have indicated that intravascular delivery of radioactive radiation is a promising solution to the restenosis enigma.
Delivery of radioactive radiation have been proposed as a means to prevent or reduce the effects of restenosis. For example, U.S. Pat. No. 5,199,939 to Dake et al. suggests that intravascular delivery of radiation may inhibit restenosis. Dake et al. suggest delivering radiation within the distal portion of a tubular catheter. Use of radioactive pellets, or, alternatively, liquid gas or powder, is also suggested. Fischell, in the publication EPO 0 593 136 A1, suggests placing a thin wire having a radioactive tip near the site of vessel wall trauma for a limited time to prevent restenosis.
Since radioactive radiation prevents restenosis but will not dilate a stenosis, radiation is preferably administered during or after dilatation. European Patent No. 0 688 580 to Verin discloses a device and method for simultaneously dilating a stenosis and delivering radioactive radiation. In particular, Verin ""580 discloses a balloon dilatation catheter having an open-ended lumen extending therethrough for the delivery of a radioactive guide wire.
Other methods of providing radiation to treatment sites have been proposed. Thornton et al., in the PCT publication WO 96/17654 describe an inflatable treatment balloon which is inflated with a liquid containing suspended radioactive materials such as I125 or P32. Walker et al., in PCT publication WO 96/13303, suggest forcing radioactive capsules or pellets through a catheter using fluid pressure to arrive at the treatment site.
What would be desirable is a non-wire based, non-hydraulic, non-pneumatic device providing simple, rapid and controlled delivery and withdrawal of radiation to a treatment site within the human body. A radioactive device allowing use and re-use without sterilization would be desirable.
The present invention includes devices and methods for providing radiation to the interior of the human body. One application is the irradiation of stenosed blood vessel regions in conjunction with angioplasty to inhibit restenosis. A preferred embodiment of the device includes a string having a first region, a second region, and an intermediate region, with radioactive material within the first region. The device can further include an elongate shaft having a proximal region and a distal region, with a string return or looping member disposed in the shaft distal region. The string can be manipulated between a first position, where the radioactive string region is located near the proximal shaft region, and a second position, where the radioactive string section is located near the distal shaft portion, near the site to be treated. The string can be manipulated by pulling the string. While the string radioactive region is in the first, proximal position, the radioactive string region is preferably housed in a radiation shielding enclosure or vault. The radioactive source preferably includes Nickel-66 formed into beads which are disposed on a KEVLAR string.
In one embodiment, the string has two free ends extending through a second string aperture in the radiation vault, with the free ends being sufficiently long to allow manipulating the string between first and second positions by pulling one of the string free ends proximally. The string free ends preferably have handles attached and the vault preferably has the second string aperture suitably sized to prevent the radiation beads from exiting the vault proximally.
In one embodiment, the device has the string disposed within a single catheter lumen closed at the distal end, allowing use and re-use of a non-sterile string and radiation source within a sterile catheter. Another device includes two catheter string lumens separated at least in the distal region by a wall. The wall distal end can terminate internally, short of the catheter distal end, and can serve as the return member, allowing the string, extending distally in one lumen, to loop and return proximally through the other lumen.
The string in the present invention can be a continuous loop or a string segment having two ends, separated proximal of the radioactive region. The string can be formed of braided KEVLAR or another polymer weave or braid resistant to degradation by radioactive isotopes. The string can be manipulated by manually pulling the string through a window in the catheter proximal region. The string can be manipulated in some devices by looping the string around one or two proximally positioned pulleys. In some embodiments, the pulleys are spring biased or motor driven. Some embodiments allow for pulling only the string radioactive region into the vault, while others support pulling the catheter proximal portion into the vault, having the string radioactive region disposed within.
In an alternate embodiment of the invention, the string is disposed within a catheter having a string lumen, with the string having a stop or stop member affixed to the string distal region. The radiation source can be a radiation tube adapted to slide over the string within the string lumen. The radiation source can be advanced distally with an elongate pusher tube adapted to slide over the string within the string lumen and push the radiation tube distally until reaching the stop. One embodiment includes a distal looping member within the catheter, where the stop can be a bead, sized to engage the radiation tube distal end and affixed to the string. The radiation tube can be retracted by pulling the string, attached bead, and engaged radiation tube proximally.
Another alternate embodiment utilizes a pusher tube having a distal end adapted to secure the proximal end of the radiation tube. Threaded and snap fittings can be utilized. The pusher tube can be used to push the radiation tube distally, with the threads, snap fittings, or other securing means being engaged only to retract the radiation tube. A preferred radiation tube is a polymeric tube including radioactive beads having lumens therethrough.
In use, the device, as provided to the treating physician, can include the string radioactive region in a proximal position relative to the catheter and within the vault. The string first region extends distally, the intermediate region loops over or through the catheter distal return member, and the second region extends back proximally along the catheter. The device can be advanced within the patient to the tissue site to be irradiated. With the device distal region in place near a site, such as a recently dilated stenosis, the string radioactive region can be quickly advanced to the device distal region. After the desired exposure period, the string radioactive section can be quickly withdrawn proximally into the vault. The quick movement of the string allows for minimizing irradiation of tissue along the catheter path. The polymer string allows use of a non-wire material that can readily navigate tight turns at the catheter distal end.